Ducted fan air-vehicles, such as an Unmanned Aerial Vehicle (UAV), may have at least one ducted fan and a fan engine to drive the fan blades. Ducted fan air-vehicles are well-know for performance capability in multiple flight conditions. For instance, ducted fan air-vehicles have the ability of forward flight and are well known for stationary hovering aerodynamic performance.
FIG. 1 is a pictorial representation of a typical ducted fan-air vehicle 100. The ducted fan air-vehicle 100 includes an air duct 102 having a duct lip 104 and a fan 106 located within the air duct 102. The ducted fan air-vehicle may have a center body 108. The center body 108 may be a housing that contains other components of the air-vehicle 100. The center body 108 may contain an engine for powering the air-vehicle 100. The center body 108 may contain additional components for air-vehicle operation, such as an avionics system.
The ducted fan air-vehicle 100 may also include a stator assembly 110 and vanes 112 for providing thrust vectoring. The stator assembly 110 and vane 112 may be located under the fan 106 located within the air duct 102. The stator assembly 110 may be located just under the fan 106 in the air duct 102 to reduce or eliminate the swirl and torque produced by the fan 106. The vanes 112 may also be placed under the fan 106. For instance, the vanes 112 may be placed slightly below an exit section 114 of the air duct 102. The air-vehicle 100 may contain fixed and/or movable vanes 112 to perform thrust vectoring for the air-vehicle 100.
In order to be effective and controllable in multiple flight conditions, ducted fan air-vehicles such as air-vehicle 100 preferably have clean and attached air flow around the duct lip in the multiple flight conditions. Further, ducted fan air-vehicles preferably have a favorable center of gravity in order to be effective and controllable. A uniform inflow velocity profile into the fan is also desirable to minimize the acoustic signature of the duct-fan interaction.
Additionally, ducted fan air-vehicles may need to carry a variety of components when in operation. For instance, in operation ducted fan air-vehicles may need to carry, without limitation, visual sensors, infrared sensors, cameras, radio communication devices, inertial sensor units, ground level sensor units, and/or payload. Due to the limited size of the ducted fan air-vehicle, in order to store the variety of units in the ducted fan, the units may be placed in external pods that are attached to the ducted fan air-vehicle. These pods may (i) cause a shift in the center of gravity, (ii) create negative interference with airflow characteristics inside the duct by blocking air intake and exhaust, and (iii) create additional drag on the UAV when the UAV is in forward flight. Additionally, the added weight of the equipment may require additional engine capacity and fuel storage capacity. It may be beneficial to increase the volume within the duct lip in order to decrease or eliminate the need for external pods while maintaining the aerodynamic requirements of a ducted fan air-vehicle.
Therefore, it would be beneficial to provide a ducted fan air-vehicle with a duct lip shape that allows for increased volume within the duct lip while still meeting the aerodynamic, center of gravity, controllability, acoustic, weight, and drag requirements of a ducted fan air-vehicle.